Pulse-echo control system



June 17, 1947. A. v. BEDFORD PULSE-ECHO CONTROL SYSTEM 2 Sheets-Sheet 1 Filed Oct. 19, 1942 TAHIVSIW T 75 attorney June 17, 1947. v A. v. BEDFORD 2,422,333

PULSE-ECHO CONTROL SYSTEM Filed on. 19, 1942 2 Sheets-$11961. 2

. l ammo Ava m2 1 mo POE-MAE L I L ZSnoentor aiented June 17, 1947 PULSE-ECHO CONTROL SYSTEM Aida V. Bedford, Princeton, N. J., assignor to Radio Corporation'of America, a corporation of Delaware Application October 19, 1942, Serial No.462,644

12 Claims.

My invention relates to pulse-echo systems and particularly to systems wherein an antenna system and/or guns or the like are moved automatically to a position determined bythe location of an object relative to the radiation pattern of the antenna system. The invention will be described specifically as applied to a radio pulse-echo system wherein the transmitter radiates signals from antennas having overlapping directional radiation patterns.

An object of the invention is to provide an improved system of the above-mentioned type.

A further object of the invention is to provide an improved system for aiming guns at an object automatically in accordance with its location with respect to overlapping radiation patterns.

A still further object of the invention is to provide an improved system for producing control signals in accordance with the location of an object with respect to overlapping radiatiqn patterns.

A still further object of the invention is to provide an improved system of the above-mentioned type which employs an alternating-current drive.

In a preferred embodiment the invention is applied to a pulse-echo system having a directive antenna system so designed that its radiation pattern or patterns may be rotated in both a horizontal plane and a vertical plane to search for an object such as an enemy airplane. The antenna system may consist of four directive antennas which may be keyed successively, as described, for example, in Patent No. 2,412,702, issued on December 1'7, 1946, in the name of Irving Wolff, and entitled Object detection and location,

or an antenna. system may be employed which is keyed by means of shorting condensers as described and claimed in Patent No. 2,400,736, issued on May 21, 1946, in the name of George H. Brown, and entitled Antenna systems.

In the receiver, control signals are derived from the four groups of pulses that have been reflected successively from the target or other object as the antennas are keyed. These groups of pulses, after demodulation, are applied to a peak measuring circuit that is switched alternately to amplifier tubes having storage capacitors in their input circuits. This switching is in synchronism with the keying of the directive antennas. The received pulses of one group charge their respective capacitors to potentials having values depending on the pulse amplitude and the control grids of said amplifier tubes are held at these capacitor potentials until the next group of pulses is applied. As a result, square wave voltages appear in the amplifier tube output circuit which are connected to suitable'A-C. amplifiers. Alternating currents of sine wave form appear in the A.-C. amplifier output circuits. 'These currents are supplied to reversible A.-C. motors for positioning the antenna system and/or the guns or other units to be controlledi As will be explained hereinafter, the phase of the square wave voltage and of the sine wave current is determined by the relative amplitudes of the received reflected pulses in the two horizontal radiation patterns and by the relative amplitudesof the received reflected pulses in the two vertical radiation patterns. The A.-C.output of each amplifier hasyone phase relation if the center of the radiation pattern is on one side of the target and it has the opposite phase relation if said center is on the other side of the target. Therefore, the A.-C. motor for either train or elevation controlwill reverse if the center of the radiation pattern for the corresponding pair of antennas swings from one side of the target to the other side. When the center of the radiation pattern is onthe target, the'A.-C. supplied to the motor is zero and the motor stops.

The invention will be better understood from the following description taken in connection with the accompanying drawing in which Figure 1 is a circuit diagram of one of the preferred embodiments of my invention; Figure 2 is a diagram of the radiation patterns of the directive antennas employed in the system of Fig. 1; and

Figures 3 to 8 are graphs that are referred to in explaining the invention. In the several figures like parts are indicated by the same reference characters.

Figure 1 shows a radio pulse-echo system comprising four directive antennas H), II, l2 and I3 for radiating the pulse energy slightly upward, downward, to the right and to the left, respectlvely, with respect to a central common axis. as indicated by the letters U, D, R and L. Tosimplify the drawing, these antennas are shown as dipoles having parabolic reflectors. The radiation patterns for these antennas are overlapping conical patterns of the character indicated in Fig. 2 where the patterns marked U, R, D and L correspond to the antennas similarly marked in Fig. 1. It is understood that the antenna radiation is greatest in the axis and weakens toward the surface of each of the cones. The antennas 10, ll, l2 and i 3 may be like those illustrated in the above-mentioned Wolfi or Brown patents, or of any suitable type, and in the particular system being described are mounted on a gimbal so that they may be moved to make their radiation patterns scan both horizontally and vertically.

High frequency radio pulses are supplied successively to the U, R, D and L antennas from a transmitter l6 through cam operated switches ll, |8, l9 and 2|, respectively, driven by a synchronous motor 22. The said pulses are obtained by modulating the high frequency carrier wave produced at transmitter l6 by means of keying pulses from a source 23. The source 23 may be a multivibrator supplying pulses recurring at the rate of 4.1 kilocycles per second, for example.

The receiver 24 demodulates the reflected pulses of high frequency (4.1 kc. in the example assumed) energy to supply pulses 21 to a detector or rectifier 26 which preferably is of the peak rectifying type. The tube 26 may be biased beyond cut-oil" by a battery 25 as illustrated or it may be grid-leak biased to provide peak detector action as is well known in the television art. The output of rectifier 26 is supplied through a large capacity blocking capacitor 3| and a switch 32 to capacitors 38 and 39, respectively, connected across the input circuits of amplifier tubes 43 and 44. The switch, 32 comprises commutator segments 33, 34, 36 and 31 and brushes ,4| and 42. The output from rectifier 26 is represented by the graph 5| where the four groups of filtered or integrated pulses of unequal amplitude are indicated at U, R, D, L. The same output as it appears on the other side of capacitor 3| is shown in Fig. 3.

The anode circuits of the tubes 43 and 44 are connected to A.-C. amplifiers 53 and 54 which drive A.-C. motors BI and 62, respectively, in the particular example illustrated. These motors rotate' in one direction or the other when theradiation pattern is oil the target and stop when it is on the target, as will be explained in connection with Figs. 3 to 8. As indicated by the legends, motors 6| and 62 are mechanically coupled to the elevation controlling and train controlling shafts 63 and 64, respectively, of the antenna supporting gimbal whereby the antenna radiation pattern is made to follow automatically an airplane or other object. The motors 6| and 62 may also control the elevation and train of one or more guns or search lights (not shown) whereby they are held on the airplane or other target automatically by means including the described servo system.

The switch 32. is driven by the motor 22in.

synchronism with the antenna cam switches l1. l8, l9 and 2|. Thus, in the diagram the up antenna switch I! is closed, the corresponding switch segment 33 of the control circuit is in contact with brush 4| to complete a circuit to the tube 43 and all other switchsegments are out of contact with the brushes. Next, as the switch 32 is rotated, the cam switch. !8 closes and the segment 34 comes into contact with brush 42 to complete a circuit to the tube 44. The switching sequence in this particular example is U, R, D, L as will be apparent from the shape of the cams and from the direction of rotation indicated by the arrows. The complete switching cycle may occupy /60 second, for example. Y

.The particular graph shown at 5| represents a condition where the radiation pattern of the antenna system is not centered on the target. It will be noted that the group of reflected pulses during the interval U are of greater amplitude than during the interval D, and that during the interval R they are of less amplitude than during the interval L. During the time segment 33 is in contact with brush 4|, the capacitor 38 is charged to a voltage equal to the peak voltage of the U group of reflected pulses; after the segment 33 rotates out of contact .with the brush 4| the capacitor 38 retains this change. When segment 33 next comes into contact with the brush 4|, the capacitor 33 either acquires more charge or loses some charge if the peak amplitude of the pulses has changed. Similarly, the other capacitor 39 is charged by the received pulses so that the voltage thereacross corresponds to the peak amplitudes of the pulses in groups R and L. The switch segments 33, 34, 36 and 31 preferably make contact with the brushes shortly after the beginning of intervals U, R, D and L of graph 5|, respectively,'and break contact shortly before the end thereof. It may be noted that the time scales for graphs 5| and 21 differ greatly, the pulse?! actually being very short compared with thein'terval U, for instance.

The application of the pulse groups U and D to the amplifier tube 43 produces the squarewave voltage 45 (Fig. 4) which appears at the anode of this tube. It will be noted that because of the stored signal in capacitor 33, the positive portion of the wave 45 produced by the U group of pulses holds over until the D group of pulses occur, this being a feature that is desirable but not essential to the operation of my system. The

negative portion likewise holds over until the next group of U pulses occurs. Similarly, the application of the pulse groups R and L to the amplifier tube 44 produces the square-wave voltage 50 (Fig. 5) which appears at the anode ofthis tube.

The square-wave voltages 45 and 56 appear in the output circuits of amplifiers 53 and 54 substantially as the sine wave voltages or currents indicated by the broken line curves 45a (Fig. 4) and 56a (Fig. 5), respectively. These sine wave voltages or currents drive the motors 6| and 62 in one direction or the other depending upon the phase of the voltage since the A.-C. field supply is synchronous with the A.-C. current supplied to the motor armatures.

Assume that the location of the target or other reflecting object with respect to the antenna radiation pattern is such that the four groups of pulses supplied to the switch 32 are as shown in Fig. 6. Now the U and D groups produce the square wave signal 55 as shown in Fig. 7 to supply the sine wave voltage 55a to the motor 6|. It will be noted that the voltage 55a is degrees out of phase with the voltage 45a previously supplied to motor 6|. 'Thus the change from the signal of Fig. 3 to that of Fig. 6 reverses motor 6|. By means of this action the antenna system is adjusted about its elevation control axis until the radiation pattern is centered vertically with respect to the target.

The R and L groups of Fig. 6 produce the square-wave voltage 60 and the sine wave voltage 60a of Fig. 8. In this particular example, the voltage 69a supplied to motor 62 is 180 degrees out of phase with respect to the voltage 50a previously applied to the motor whereby the motor 62 reverses. Thus the antenna system is adjusted about the train control axis 64 until the radiation pattern is centered horizontally with respect to the target.

An important feature of the invention is that the system is not affected muchby noise signals because the capacity of the capacitors 38 and 39 is so large that their charge is changed a negligible amount by such signals. Expressed another way, the capacitors reduce the noise by reducing the net band-width of the signal used. However, the time constant must not be made too long or hunting of the servo system may occur due to the delay of the signal.

It should be understood that the invention is not limited to a system employing four radiation patterns as it is equally applicable, for example, to a system having only left-right control or indication'. Also, the radiation patterns may be produced by sound or light radiation, for example, rather than by radiation of radio signals, my capacitor-switching receiving system being equally applicable to all such systems. p

I claim as my invention:

1. In a servo system, means for transmitting pulses and receiving echoes alternately for short intervals from an assembly of two directive radiradiator, an electric motor, and utilizing means for driving said motor backward or forward in accordance with the relative amplitudes of the voltages appearing successively across said can-- denser, and. means whereby said motor turns said assembly vof radiators toward said source of echoes.

2. In a system wherein groups of pulses are received alternately, a vacuum tube having a capacitor connected across its input electrodes, switching means associated with said capacitor, means for passing direct current pulses representative of said alternately-occurring groupsof pulses only through said switching means to charge said capacitor whereby a substantially square wave voltage appears thereacross, means for making said switching means eiiective to pass current to said capacitor synchronously with the reception of said groups of pulses, an electric motor of the type that reversesiwhen an alternating current applied thereto is reversed in phase, an alternating current amplifier connected to said motor to supply alternating current thereto, and means for supplying said square wave voltage to saidlarhplifier;

3. Ina receiver for receiving reflected pulses in a system wherein pulses of energy are transf mitted in a pair of overlapping radiation patterns, each pattern including a group of pulses, the said radiation patterns being radiated in succession, means for obtaining from said'refiected pulses a signal having repeating voltage levels, a capacitor, a vacuum tube having input electrodes connected across said capacitor, means for connecting said first means to the input electrodes of said vacuum tube, said connection being mad in synchronism with and only during the radiation of said pair of patterns whereby a square wave voltage appears across said capacitor, an alternating current motor of the type that reverses when alternating current applied therepatterns, a radio pulse transmitter, means for switching said antennas successively to said transmitter whereby pulses are radiated to a re-.

fleeting object, a. receiver for receivingpulses reflected from said object, a capacitor, switch ing means for successively applying said received pulses to said capacitor for producing a square wave voltage thereacross, an alternating current motor of the type that reverses whenthe .alternating current supplied thereto is reversed i in ph'ase, means for amplifying the fundamental frequency component ofsaid square wave voltage, and means for driving said motor by said amplified voltages 5. In a radio pulse echo system, a pair oi. di-

rective antennas having overlapping radiation patterns, a. radiopulse transmitter, means for switching said antennas successively to said transmitter, a receiver including means for obtaining a voltage that is a measure of theamplitude of the group of refiectedpulses of one radiation pattern andiorobtaining a voltage that is a measure of the amplitude of, the" group of reflected pulses of the other "radiation pattern, a capacitor, switchingmcans for successively applying said two voltages only to said capacitor for producinga square wave voltage thereacross,

ing two voltages which are a measure of the amplitude of the two groups of reflected pulses, respectively, a capacitor, switching means for successively applying said two voltages only to said capacitor ,for producing substantially a versed in phase, means for amplifying said square to is reversed in phase, and means for applying the fundamental frequency component of said square wave voltage to said motor.

4. In a, radio pulse echo system, a'pair of diwave voltage, and means for driving saidmotor by said amplified voltage. e I 7. In a pulse-echo'servo system, an assembly of radiators, means for producing an alternating-current wave consisting of four repeating voltage levels having amplitudes corresponding inversely to the angular displacement 'of said assembly of radiators from arefiecting target in the directions upward in the vertical plane, to the right in the horizontal plane, downward and to the left, respectively, an-amplifier, synchronous switching means for connecting said source of alternating-current wave to said amplirler only. during the time of the voltage levels corresponding tosaid displacements in one of said planes, a reversible alternating-current motor having an alternating-current field supply a synchronous with said alternating-current wave, and means for supplying the output of said amplifier to said motor, saidmotor being mechanically coupled to said assembly of radiators to turn it toward said target.

8. In a, pulse-echo servo system, an assembly of radiators, means for producing an alternatingcurrent wave consisting of four repeating voltage levels having amplitudes corresponding inversely to the angular displacement of said assembly of rective antennas having overlapping radiation radiators froma reflecting target in the directions the time of the voltage'levels corresponding to said displacements in one of said planes, a reversible alternating-current motor having an alternating-current field supply synchronous with said alternating-current wave, and means for amplifying the fundamental alternating-current component of voltage acrosssaid capacitor and applying'said voltage to said motor, said motor being mechanically coupled to said assembly of radiators to turn it toward said target.

9. In a pulse-echo servo system, an assembly of radiators, means-for producing an alternatingcurrent wave consisting of four repeating voltage levels having amplitudes corresponding inversely to the'angular displacement of said assembly of radiators from a reflecting target in the directions upward, to the right, downward and to the left, respectively, a capacitor, synchronous switching means for connecting said source of alternatingcurrent wave across said capacitor only during the time of the voltage levels corresponding to said displacements to the right and to the left, a reversible alternating-current motor having an alternating-current field supply synchronous with said alternating-current wave, and means for amplifyingthe fundamental alternating-current component of voltage across said capacitor and applying said voltage to said motor, said motor being mechanically coupled to said assembly of radiators to turn it toward said target.

10.'In combination, a pair of alternating current motors of the type that reverses when alternating current applied thereto is reversed in phase, means for obtaining alternately occurring first and second voltages each having an amplitude with respect to ground potential representative of the direction in which it is desired'to drive one of said motors, means for obtaining alternately occurring third and fourth voltages each having an amplitude with respect to ground potential representative of the direction in which it is desired to drive the second motor, said voltages occurring in the sequence of first, third, second and fourth voltages, means for amplifying the fundamental frequency component of the alternating-current wave formed by said first and second voltages to the exclusion of said third and fourth voltages to obtain alternating current, means for applying said alternating current to said first motor, means for amplifying the fundamental frequency component of the alternatingcurrent wave formed by said third and fourth voltages to the exclusion of said first and second voltages to obtain a second alternating current,

and means for applying said second alternating a current to said second motor.

11. In a radio pulse-echo system, a receiver, an assembly ofdirective antennas having overlapping radiation patterns in the horizontal plane and having overlapping radiation patterns in the vertical plane, means for'switching said antennas successively for supplying to said recelver an alternating-current wave consisting of fier, switching means for successively applying said alternating-current wave to said amplifier only during the time of the two voltage levels corresponding to angular displacement in the horizontal plane, a secondamplifier, switching means for successively applying said alternatingcurrent wave to said second amplifier only during the time of the other two voltage levels, a pair of alternating current motors connected to receive current from said first and second amplifiers, respectively, said motors being of the type that reverses when the alternating current supplied thereto is reversed in phase.

12. In a servo system, means for transmitting pulses from an assembly of directive radiation means for radiating successively overlapping radiation patterns in a horizontal plane and in a vertical plane, means for receiving said pulses after reflection from an echo source, said radiation patterns having characteristics such that the received signal difiers in strength for the successive radiations in accordance with the displacement of the assembly of the radiation means with respect to the source of the echoes, two capacitors, switching means synchronized with the transmitting and receiving means for charging each of said capacitors in accordance with the received signals during the interval of transmission by radiation in each of said planes, respectively, two alternating current motors, and utilizing means for driving each of said motors backward or forward in accordance with the phase of the voltage across eachof said capacitors, respectively, and means whereby said motors turn said assembly of radiators toward said source of echoes.

ALDA V. BEDFORD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,976,648 Wittkuhns Oct. 9, 1934 2,300,742 Harrison et a1 Nov. 3, 1942 1,959,804 Wittkuhns et a1 May 22, 1934 

